11

Storage of Radioactive Material and Waste Management

2 STORAGE OF RADIOACTIVE MATERIAL AND WASTE MANAGEMENT

Contents Page

11.1 Storage of radioactive material11.1.1 Introduction.................................................................311.1.2Low and high level radioactive waste...........................411.1.3Storage of high level wastes........................................5

11.2 The principles of disposal11.2.1 Introduction.................................................................611.2.2Delay and decay..........................................................911.2.3Dilute and disperse......................................................911.2.4Concentrate and contain............................................10

11.3 Disposal of specific waste types11.3.1Low activity waste disposal - solid waste....................1011.3.2Low activity waste disposal - liquid waste...................1111.3.3Material for incineration.............................................1311.3.4Airborne waste..........................................................13

11.4 Packaging radioactive waste for transport and thendisposal.............................................................................14

STORAGE OF RADIOACTIVE MATERIAL AND WASTE MANAGEMENT 1

STORAGE OF RADIOACTIVE MATERIAL AND WASTE MANAGEMENT 3

11.1 Storage of radioactive material

11.1.1 Introduction

Storage of radioactive material becomes necessary before and after usage. Radioactive material received from a supplier has to be initially stored until needed. Often bulk radioactive materials purchased are stored in a store in close proximity to the laboratory and amounts removed from time to time as necessary as it is not advisable to keep bulk radioactive material in an area where workers spend long periods of time. Waste arising out of the usage of radioactive material have to be stored until they are disposed of, removed for disposal, sent for interim storage or placed on long term storage.

Storage of radioactive materials must be done so that they present no hazard to persons in the vicinity and are secure against theft or unauthorized tampering. Materials not in regular use should be kept in a locked store. Radiation levels outside the store should not normally exceed 2.5 Sv/h. Not all materials, however, need be put into storage every night; for example, to do so with highly toxic alpha emitters could be more hazardous than to leave them in the glove box where they are normally handled. All containers of radioactive material placed in storage must be adequately labelled. Where the radioactive material stored is likely to evolve a radioactive gas or vapour, the store should have separate and adequate mechanical ventilation to the outside air. The fan should operate for at least 2 minutes before any person enters or opens the store.

Unsealed radioactive residues at tracer level may be stored in glass vessels with polyethylene, rubber or cork stoppers.

Ionizing radiation may induce decomposition of water, hence vented containers may be needed to store aqueous radioactive solutions. Chemically stable solutions containing about 200 MBq of alpha activity or 2 GBq of beta activity normally produce about 1 ml per month of gas at NTP. Bottles of old radioactive liquids should be opened only in a fume cupboard.

Thermally unstable radioactive solutions, eg. nitric acid or other oxidizing solutions containing traces of organic material, peroxides or chlorates, need particular care and should always be stored in vented containers. Consideration should be given to neutralizing acidic or alkaline waste before disposal.

Containers used to transfer radioactive materials to and from the store should be designed to reduce the dose equivalent rate at 1 m from the surface to not more than 100 Sv/h and should be constructed to prevent accidental release of the material if they are dropped or upset.

A radiation warning sign should be displayed at the entrance to each radioactive store.

STORAGE OF RADIOACTIVE MATERIAL AND WASTE MANAGEMENT 5

Every radioisotope user must monitor his radioactivity inventory at a minimum and dispose of material no longer required by:

- disposing of the material whose activity is sufficiently low to permit disposal;

- placing in interim storage, any material which is short lived and will decay to a level that will warrant disposal after a period of storage not longer that one year, or

- arranging to place in a long term store any material with a half-life, activity or toxicity that will not permit it to be disposed of within a year.

11.1.2 Low and high level radioactive waste

Radioactive waste comes in a wide variety of chemical forms and activities. Waste can roughly be divided into two categories: high and low activity.

Low activity waste basically includes all material whose activity does not exceed the limits of discharge specified for the radionuclide in the ICRP recommendations. This will include: samples which have been prepared for gamma or liquid scintillation counting, some disposable materials used in handling unsealed sources (these include a range of articles from tissue, rubber gloves, syringes, pipettes to broken glass ware) and pieces of equipment. These must be checked for activity before disposing as low activity waste. As a rough "rule of the thumb", items with a surface count rate <200cps or where the surface dose rate is <5 Sv per hour, can be described as low activity.

High activity waste basically takes in the remainder including unused stock solutions, early rinsing through ion exchange columns and the column itself, materials used for handling stock solutions and during iodination procedures.

The process of waste management while adhering to the ALARA principle must start at the point of origin of the waste. Collecting the low level waste at the point of origin must be in easily disposable bags, to enable minimum handling and no contamination. Foot-operated waste bins with removable bucket or bag should be used for solid active material.

Management of low level waste is facilitated by segregating the waste, at the point of arising into wastes of different specific activities, combustible and non combustible material, and disposable dates of each package. Storage of such waste is an interim solution to the radioactive waste management problem. Low level low activity university and hospital waste may be disposed of with ordinary trade waste. The principle used here is dilution, the odd

package containing a small quantity of radioactive material being well diluted among the vast quantities of trade and domestic waste on the local refuse tip.

STORAGE OF RADIOACTIVE MATERIAL AND WASTE MANAGEMENT 7

Solid radioactive waste (tissues, pipettes, etc) may be stored temporarily in a suitable shielded container in the laboratory until the experiment is finished, and then removed to an appropriate storage area to decay. Low activity waste may be placed in plastic lined "garbags" which should be correctly labelled with the name of the user, date, nuclide and activity, and clearly marked with the radiation hazard symbol. Combustible and non-combustible materials must be placed in separate containers.

Low activity waste may be disposed of immediately, whereas high activity waste disposable after a period of decay, should be held in interim storage to allow them to decay to activities low enough to permit disposal by burial, incineration or release to sewers.

11.1.3 Storage of high level wastes

The following applies for the storage of high activity waste disposable after a period of storage:

(a) Facilities shall be available for the safe removal and storage of radioactive waste, which enables a minimum of handling and minimizes exposure to personnel. These facilities shall be used when removing radioactive waste to long term storage, or when handling waste within the store.

(b) Generally high activity waste will:

- Occur in smaller amounts than low activity waste- Have high specific activities- Require shielding- Not be released to the environment until sufficient decay has

taken place and thus becomes low activity waste- Comprise all materials intimately connected with stock

solution, such as vials pipettes, syringes, gloves etc.

(c) High activity waste should be contained according to decay rate. Those nuclides whose half life is expressed in hours and days must be segregated and contained separately from nuclides whose half life is expressed in months.

(d) High activity waste should be contained according to its physical state. Wherever possible, liquid, solid and gaseous waste will be contained separately. Any solid or liquid waste producing a gaseous component should be sealed in at least one airtight plastic bag.

(e) High activity solid waste should be contained in small volume, disposable containers for ease of handling and storage.

(f) High activity solid waste should be double bagged in heavy duty plastic bags to ensure adequate containment. Both bags should be secured tightly with twine or tape.

(g) Waste should be contained where possible in standard cardboard boxes of the self-locking type or sharps containers to avoid puncture by glassware etc. All needles must be capped or placed in an approved sharps container before disposal. Boxes should be taped securely before disposal.

(h) When more than one containment vessel is required, the internal containers as well as the external containers should be labelled.

(i) High activity waste should be stored, removed and handled under shielding such that any exposure is reduced to a minimum.

(j) High activity waste should be inventorised such that each stock container ordered has a known date of disposal.

(k) High activity waste may be contained and stored and shielded in a designated waste storage area for the department/laboratory.

(l) Animal carcasses containing short-lived radioactivity should be stored in a freezer in bags properly shielded and labelled. After the appropriate decay time, the waste is to be incinerated or buried under the supervision of the RSO in accordance with requirements for disposal.

(m)High activity liquid waste must be left to decay in suitably shielded and labelled containers in the laboratory or a holding tank or where possible diluted in line to low specific activities that warrant immediate disposal. Abundant quantities of carrier solution should be used, in addition to water, for dilution where necessary.

(n) Where delay tanks are used to store liquid effluent before discharge into the drains, the contents must be mixed, diluted and sampled to ensure compliance with disposal requirements.

(o) Organic liquids must be collected and stored in separately labelled glass containers.

(p) Scintillation vials containing 3H, 14C, 32P, or 35S must be placed in drums or bags and properly shielded and labelled. Vials must not be allowed to accumulate in the laboratory as they are both a fire and health hazard.

11.2 The principles of disposal of radioactive waste

11.2.1 Introduction

STORAGE OF RADIOACTIVE MATERIAL AND WASTE MANAGEMENT 9Residues of radioactive materials and wastes resulting from the

use of such materials in hospitals, factories, research and teaching institutions as a result of the many applications of radiation, have to be managed in a manner acceptable to the society.

The activity and the half-lives of such materials are far lower than the high level waste that arise in nuclear reactors. Their disposal can be effected through the normal refuse collection or sewage systems. Although radioactivity will ultimately decay, their disposal cannot always await decay due to very long half-lives of many radionuclides.

There are three general approaches to the management of radioactive wastes:

(a) Release and dispersal into the environment.(b) Storage.(c) Disposal.

Of course, release of radioactivity to the environment might reasonably be thought to constitute disposal. However, it is useful to distinguish between deliberate dispersal and methods of disposal involving irretrievable placement of wastes so that they are isolated, at least temporarily, from the environment.

Storage of radioactive waste is an important procedure when dealing with nuclides of relatively short half-life (eg. up to a few months). Storage or hold-up of the waste for a period of up to a few years may reduce the activity to a sufficiently low level to permit release to the environment or, in the case of solid waste, to facilitate disposal.

The approach selected in a given situation depends on many factors such as the quantity and type of radioactivity, its physical and chemical forms and the geographical location.

Any release of radioactivity is a potential source of radiation exposure to the population at large. The radiation exposure can occur via many different exposure pathways. Consider, for example, a release of activity from a chimney stack. This would be dispersed by air movements and could result in radiation exposure of the population in a number of ways:

(a) direct external - or -radiation from the plume;

(b) inhalation of radioactivity resulting in internal dose;

(c) direct external - or -radiation from deposition (fall-out) of radioactivity;

(d) consumption of foodstuffs (eg. vegetables) contaminated by deposition; and

(e) consumption of meat or milk from animals which have grazed on contaminated ground.

STORAGE OF RADIOACTIVE MATERIAL AND WASTE MANAGEMENT 11

Similarly, radioactivity discharged into a river, lake or sea could result in a number of exposure pathways:

(a) contamination of drinking water supplies;

(b) external dose to swimmers or to people using contaminated beaches; and

(c) consumption of contaminated fish, shellfish or plants.

Some of these exposure pathways result from complex routes known as food chains. For example, activity discharged to the sea may be taken up by plankton which are eaten by fish, which are in turn eaten by man. An example of a simple marine food chain is illustrated in figure 10.1.

Figure 11.1. A simple marine food chain.

In a given situation it is often found that one particular pathway is much more important than any other. That is, it results in much higher radiation dose, sometimes to quite a small group of people. This is called the critical exposure pathway and the group of people which receives the highest dose from this pathway is known as the Critical group. The importance of the critical exposure pathway is that the quantity of radioactivity discharged must be controlled so as to limit the dose to the critical group. The critical group in any particular case depends on the mode of release, the nuclides involved, local ecology (eg. forms of marine life, etc.) and local habits.

An important example of radioactivity uptake is the uptake of radioactive iodine. Iodine taken into the body gets concentrated in the thyroid. In a release of radioactive iodine to the atmosphere the uptake may be due to inhalation of airborne iodine or consumption of milk from cows which have grazed on contaminated pasture. In either case, exposed children comprise the critical group because of the relatively large intake by children in proportion to the size of the thyroid.

To deal with such situations, discharge limits are set so that the critical group receives doses well below the permissible level.

The fundamental objectives of waste management are to ensure that wastes do not pose an environmental problem either in the short or long term and that no one is subject to any health risk.

To achieve this objective, effective waste management principles and processes have to be used. The principles on which waste management is based are:

- Delay and decay.- Dilute and disperse.- Concentrate and contain.

11.2.2 Delay and decay

It is often found that most of the waste produced by individual users of radioactive materials contains very small amounts of short lived radionuclides. In such cases, the wastes can be stored until the activity decays to such a level that they can be considered inactive as per the local regulations and dumped with the approval of the licensing authority along with inactive refuse. This technique may be used for solids, liquids or gases. The limitation of the method is generally related to the time necessary for storage and the physical problems this may cause.

11.2.3 Dilute and disperse

The dilute and disperse mechanism is the deliberate release of waste into the environment with dilution, by air or water, to sufficiently low levels. This policy is generally limited to liquids or gases which have discharge limits that are not so conservative that they can only be reached by deliberate additional dilution processes. It is not expected that excessive dilution be used to achieve compliance with established limits, at least certainly not on any routine basis.

National and International (ICRP) limits exist for the discharge of waste to the environment. In Australia these limits are embodied in the Health (Radiation Safety) Regulations for liquid and gaseous effluents. The practice of dispersal is justified on the grounds that

STORAGE OF RADIOACTIVE MATERIAL AND WASTE MANAGEMENT 13any resulting exposures are acceptably low and that further treatment of the wastes would not result in as greater reduction in exposure.

11.2.4 Concentrate and contain

This practice can be applied to liquid wastes through chemical treatment processes and solid wastes by volume reduction techniques, the aim being to minimize volumes, and isolate and store the active component.

Containment consists of placing barriers around the waste in order to restrict the release of radionuclides into the environment. For higher level wastes, multiple barriers are used to give greater assurance of containment. The barriers used vary from specialised forms of physical containment to isolation mechanisms such as remote area storage and deep geological burial.

Radioactive waste arising from university, hospital and research work are classified as low level waste having a specific activity lower the 1GBq/m3.

11.3 Disposal of specific waste types

11.3.1 Low activity waste disposal - solid waste

Low activity waste disposal is often facilitated by segregation of the waste at the point of origin, for example into wastes of different specific activity, or into combustible and non-combustible material. Reduction of volume is often a useful procedure and this can be achieved either by compression of the waste or, in the case of combustible waste, by incineration. In the latter case, the flue gases from the incinerator must be filtered and the filters and ash then comprise the reduced volume of waste.

Low activity university and hospital waste may be disposed of with ordinary trade waste. The principle used here is dilution, the odd package containing a small quantity of radioactive material being well diluted among the vast quantities of trade and domestic waste on the local refuse tip.

Low level radioactive waste packages, properly packaged for transport and disposal should be arranged to be picked up and disposed of by a suitable contractor approved by the authority. Disposal to landfill in this manner is restricted to solid waste excluding animal carcasses.

The maximum activity of each radionuclide which may be included in any package of waste for disposal at a municipal tip is determined by its half-life and is given in terms of its current Annual Limit of Intake (ALI) by ingestion for radiation workers, as recommended by the International Commission on Radiological Protection, as follows:

STORAGE OF RADIOACTIVE MATERIAL AND WASTE MANAGEMENT 15- For radionuclides from the natural uranium or natural thorium

decay series, including the parent uranium and thorium radionuclides themselves, no more than 250 Bq of each per kg of waste.

- For other radionuclides having a half-life of 1 year or greater: 0.1 ALI.

- For other radionuclides having a half-life between 60 days and 1 year: 1 ALI.

- For other radionuclides having a half-life of 60 days or less: 10 ALI.

[Current ALI values are given in ICRP (Report 61)].

Regardless of the activities of the radionuclides contained in a package, the maximum dose rate at the surface of the package should be not more than 5 Sv/h and this should be checked with a survey meter before the package leaves the premises of the user.

There is no limit to the number of packages which may be disposed of any one time, but the total activity of each radionuclide contained in all packages placed in any one burial trench or pit should not exceed ten times the limit which may be contained in any one package, unless the prior approval of the relevant authority has been obtained.

11.3.2 Low activity waste disposal - liquid waste

Various approaches are used in the management of radioactive liquid wastes. Where the level of radioactivity is very low, liquid wastes can often be discharged either as a trade waste to sewers or directly into a river or lake, or into coastal waters. A period of storage might be necessary in order to allow relatively short-lived radionuclides to decay. In this case, a number of delay tanks may be provided and when one is full it is isolated until the activity has decayed to an acceptable level for release. Before discharge contents of the tank are stirred, sampled and analysed to confirm that it is within the prescribed activity limits.

Liquid wastes of higher specific activity may be treated by ion-exchange, evaporation or chemical treatment. These processes result in the concentration of the radioactivity from the liquid waste into a much smaller volume of residue to sludge which may be suitable for conversion into a solid waste for storage or disposal. The effluent from the process would normally be of sufficiently low activity to permit its discharge.

Discharge to sewers is a very convenient method where both the volume and specific activity are low but it is strictly controlled. The main considerations are that sewage, sewer walls and sewage works become contaminated, resulting in a hazard to sewage workers. In addition sewage sludge is often used as a fertilizer and, if it is contaminated, could result in the contamination of crops.

For low level liquid waste generated in hospitals and research laboratories the most convenient and widely used practice for

STORAGE OF RADIOACTIVE MATERIAL AND WASTE MANAGEMENT 17disposal is to discharge the wastes into sewers under controlled conditions. It is not always necessary to dilute the waste liquids before discharge because a dilution factor of at least 100 is generally obtained in the sewer before the liquid waste finally reaches the main stream. Before discharge, the specific gross activity of the liquid as well as the concentration of

individual radionuclides in the mixture should be assessed. Certain guidelines for the discharge of liquid wastes containing radionuclides are given below:

(1)A user may dispose of radioactive liquid waste into the sewer system provided the quantity and concentration are within the following limits:

- the quantity of any radioactive material released into the system in any seven day period does not exceed 20 times the Annual Limit of Intake by ingestion for that radionuclide;

- the quantity of radioactive substance discharged into that system from the premises concerned in any one period of 24 hours does not exceed the quantity which, if diluted by the average daily quantity of sewage discharged into that system from those premises, would result in an average concentration equal to the appropriate maximum concentration permitted by Part XIII of Health (Radiation Safety) Regulations 1984.

(2)All radioactive materials so released into the sewer system should be completely soluble and dispersible in water. Liquid, if it contains suspended solids or sediments, may need to be filtered prior to discharge. Non-aqueous wastes which are immiscible with water should be completely excluded.

(3)The activity of the liquid waste acceptable for disposal into the sewer system must be in accordance with the regulations of the competent authority.

(4)Acidic wastes should be neutralized and, if necessary, filtered before they are discharged into the sewage system.

(5) If the liquid discharged contains toxic or other chemicals which will adversely affect sewage treatment, the user must obtain permission from the local authorities before the liquid waste is discharged.

(6)A complete and up-to-date record of all the discharges made by the isotope user is to be maintained. This record should be available for inspection by the licensing authority at any time.

Drains used for disposing of aqueous radioactive waste should be clearly and permanently labelled, and should not be connected to non-radioactive waste lines until outside the building.

Liquid radioactive waste discharged with laboratory sinks should be diluted with copious amounts of water.

It is important that each user keeps the radioactive content of liquid wastes generated in the laboratories to the minimum. In some

STORAGE OF RADIOACTIVE MATERIAL AND WASTE MANAGEMENT 19circumstances, the wastes need to be classified at the point of origin as aqueous and non-aqueous acidic alkaline or neutral.

Acidic and alkaline wastes are best stored separately from each other and neutralised prior to disposal to the sewer.

Non-aqueous liquids should be stored separately from aqueous ones because mixing of this stream with aqueous solutions will pose problems for subsequent treatment.

Collection of low level liquid waste is best done using ten or twenty-litre polythene carboys with sealing disc and screw cap. Each container used for this purpose should be distinctly marked "acidic" or "alkaline" with proper radiation symbols pasted on. Non-aqueous waste may be stored in appropriate polyethylene or other plastic containers. If glass bottles have to be used, they should be kept in secondary containers to protect them from breaking. Since organic liquids are likely to attack polythene chemically, it cannot be used for the collection of non-aqueous wastes.

11.3.3 Material for incineration

Radioactive waste that must be disposed of by incineration includes flammable solid waste, animal carcasses, vials containing organic solvents, sharps and bulk solvents. Glass vials with closed metal caps are not acceptable because of the risk of explosion and the possibility of radioactive glass residue in the slag; the contents of these should be transferred to plastic containers for incineration.

There are only two incinerators in Melbourne that are licensed by the CPA to incinerate these types of waste.

11.3.4 Airborne waste

Releases of gaseous or airborne particulate radioactivity to the atmosphere present more direct exposure pathways than other forms of disposal and with a few exceptions, such as the noble gases, the discharge limits are quite low. The exposure pathways include external irradiation, inhalation and ingestion by various routes. The general philosophy is to reduce the activity being released to atmosphere as far as practicable and then to release it in such a way as to obtain adequate dispersal.

Radioactive waste in the form of aerosols or gases should be diluted, filtered or otherwise treated so that, at the point of discharge, the quantity discharged should not exceed the amount permitted by the Health (Radiation Safety) Regulations. Where necessary airborne waste should be monitored to ensure compliance with requirements.

Any exhaust from a radioactive laboratory, or a fume cupboard in which radioactive materials are used should be discharged into the open air. The exhaust air must be effectively dispersed to

STORAGE OF RADIOACTIVE MATERIAL AND WASTE MANAGEMENT 21atmosphere so that it is not drawn into any air intake or occupied area. For this purpose smoke and/or tracer gas tests should be carried out under the severest meteorological conditions of existing buildings. Similar tests may also be carried out on models of proposed buildings in wind tunnels.

11.4 Packaging radioactive waste for transport and then disposal

Note that the legal requirements of transport are dealt with more fully in Section 12.

Packaging of radioactive waste material for transport should be secure and so designed that the package can be easily handled. The outer layer should be of such material as to avoid, as far as practicable, the collection and retention of water, and finish so that it may be easily decontaminated. When a package requires no visible labelling implying that its contents are radioactive the outer layer of packaging should be opaque.

Radioactive waste material for disposal should be packed in closed drums, opaque plastic bags or multi-layer paper bags on the premises of the user before transport. All three forms of packaging are acceptable for disposal at municipal tips. Opaque plastic bags or multi-layer paper bags are suitable for disposal in incinerators. There should be at least two complete layers of packaging between the radioactive waste material and the exterior of the package, one layer of which shall be waterproof.

Syringe needles, pipettes tips and any other sharp objects should be adequately protected in closed drums or by means of impenetrable sleeves or sharps containers so that they will not puncture the outer package. These together with other soft waste material such as paper, cardboard, cloth and solid objects including empty vials and disposable syringes contained in plastic garbage bags used as the liner in the waste bin in the working area may be placed in a second plastic garbage bag in a clean area of the users premises with both bags securely closed to form a suitable disposable package. There must not be any contamination on the external part of the package.

Example: Iodine-125(125I) counting waste (vials and test tubes) may be disposed of as normal pathological waste. The NH&MRC allows 10 times the Annual Limit of Intake per package, provided that the surface dose rate is less the 5 Gy/hr. For 125I, this is equivalent to 10MBq. If the average radioactive iodination kit contains approximately 2.5 kBq, then a package may contain the waste from some 40 kits.